Modity the :json_data_empty attribute from `:null => false` to `:null => true`

Don't test language-level exception messages

Ruby implementations should be free to produce exception
messages that are not identical to MRI. For example,
Rubinius produces 'Expected an even number, got 5'.

to address ORA-01400 errors with Oracle enhanced adapter.

The original commit 3c0bf043 requires :json_data_empty attribute
has empty string OR null, then setting `:default => ""` is enough.

Validates_presence_of associated object marked for destruction

 will now return nil instead of raise a NoMethodError if the receiving object does not implement the method

It has been moved to active_record_deprecated_finders.

Use #to_a instead.

It doesn't serve much purpose now that ActiveRecord::Base.all returns a
Relation.

The code is moved to active_record_deprecated_finders.

Previously it returned an Array.

If you want an array, call e.g. `Post.to_a` rather than `Post.all`. This
is more explicit.

In most cases this should not break existing code, since
Relations use method_missing to delegate unknown methods to #to_a
anyway.

`:rails_env` tasks is not needed in all the tasks that depends of
`load_config`, only in the tasks that uses `Rails.env`.

Since `:rails_env` task set the `Rails.env` to be "development" if it is
not set we don't need the `||` statements too

Fix #7175.

Conflicts:
	activerecord/lib/active_record/railties/databases.rake

Modify the preference attribute from `:null => false` to `:null => true`

to address ORA-01400 errors with Oracle enhanced adapter.

Issue #4856 had been fixed and tested with
the attribute `:null => false, :default => ""`.
Now `:null => false` attribute is not necessary to test this issue.

Conflicts:
	actionpack/lib/action_controller/metal/http_authentication.rb

Refactor ActiveRecord::Inheritance.base_class logic

Fix typo in documentation

Moved logic from class_of_active_record_descendant(class) to the
base_class method. This method was confusing because it required
an argument, but that argument was 'self'.

Moved base_class tests to inheritance_test.rb and added some test
coverage for some untested cases.

Missed extend for eager_autoload

Update activerecord/CHANGELOG.md

Eager autoload ActiveRecord association helpers

Fixed markdown code indenting

Switched update_column recommendation in changelog to update_columns

Related to #7164

Looks like the last one; thanks!

Postgresql auto reconnect 2

Use string datatype for the setting attribute

to make store works all database adapters.

remove duplicate build runs in travis

test identity map and not fully removed when the feature was removed.

Closes #1190

Addresses ORA-01400 errors and also supports #6115

Replace the flush parameter with a Hash.

Issue #6115 has been fixed and tested with
the attribute `:null => false, :default => ""`
However `:null => false` attribute is not necessary to test this issue,
which causes many ORA-01400 errors with Oracle enhanced adapter.